This invention relates to a synchrotron for accelerating or accumulating charged particles such as electrons and ions, and more particularly to the miniaturization of the synchrotron.
FIG. 1 shows, for example, a conventional synchrotron shown in "The Design of Synchrotron for Incident Charged Particle", Molecular Science Research Institute (Mar. 1981). As shown in FIG. 1, an inflector 3 for letting beams supplied by an auxiliary accelerator 1 such as a linac or microtron be incident upon a vacuum chamber 4 is installed at the front end of a low energy transport pipe 2. Along the vacuum chamber 4, there are disposed perturbators 5 for shifting the orbit of incident particles, bipolar electromagnets 6 for bending the charged particles to form a closed orbit, tetrapolar electromagnets 7 for focusing the beams, a high-frequency cavity 8 for accelerating the particles, a kicker 9 for bending the orbit of beams at the time of exit, etc. A deflector 10 is used to send out exit beam to a high-energy transport pipe.
The bipolar electrodes 6 and the tetrapolar electrodes 7 located on the curved peripheries are installed at equal intervals and form a circle with six equivalents.
The beams accelerated by the auxiliary accelerator 1 are focused by the tetrapolar electromagnets 7a, 7b and introduced into the vacuum chamber 4 through the low-energy transport pipe 2 after being bent by the inflector 3. The perturbators 5 introduce the incident beams while outwardly shifting their initial orbit and gradually restoring the orbit to the inside. The incident beams are bent by the bipolar electromagnets 6 and moved in the closed orbit but focused in horizontal and vertical directions while being passed through the tetrapolar electromagnets 7 and otherwise caused to be dispersed therebetween to form a stable mode with six periods a circle.
Upon completion of the aforesaid incidence, the voltage applied to the high-frequency cavity 8 is increased to raise the energy by interlocking the intensity of the magnetic fields of the bipolar electrodes 6 and the tetrapolar electrodes 7 therewith. The kicker 9 is started at the point of time the energy has reached the predetermined level and the beams are thereby deviated from the stabilized orbit and outwardly bent at the deflector 10, whereby they are sent out to the high-energy transport pipe 11.
The beams thus taken out are allowed to divert for a short period and then introduced to a storage ring or an analyzer (not shown) while being focused by tetrapolar electrodes 7e, 7f attached to the transport pipe 11.
FIG. 2 is a diagram showing the principle of the operation of another conventional synchrotron shown in the "Journal of Japan Physical Society", Vol. 17, No. 4 (1962), pp 271-278, the synchrotron having the same construction as what has been shown in FIG. 1. As shown in FIG. 2, a bipolar deflecting electromagnets 6 form the central orbit 22 of charged particles and, along the central orbit, there are disposed an inflector 3 for making the charged particles supplied by a linear accelerator 1 incident on the synchrotron and a high-frequency cavity 8 for giving energy to the charged beams.
FIG. 3 shows a conventional bipolar deflecting electromagnet 6 equipped with deflecting coils 11 fitted to an iron core 13 by coil clasps 12 and a vacuum chamber 4 through which the charged beams pass. The charged beams supplied by the auxiliary accelerator 1 through the inflector 3 are bent in the deflecting electromagnet 6 and form the closed orbit 22 shown in FIG. 2. The curvature radius .delta. of the charged beam is proportional to the energy E thereof and inversely proportional to the magnetic field B of the deflecting electromagnet 6, i.e., EQU .delta..alpha.E/B.
When energy is applied to the charged beams by means of the hiqh-frequency cavity 8, the magnetic field of the bipolar deflecting electromagnet 6 is proportionally increased to prevent the closed orbit of the charged beams from changing. This action is generally called the acceleration of charged beams by the synchrotron. The time required for the acceleration normally ranges from 10-several 100 ms. In other words, the bipolar deflecting electromagnet 6 is excited within the time of 10-several 100 ms from a low magnetic field (generally several 10 Gauss) corresponding to incident charged beam energy up to a high magnetic field (generally over 10,000 Gauss) corresponding to accelerated charged beam energy. Consequently, the iron core 13 of the bipolar diflecting electromagnet 6 is usually of laminated construction. FIGS. 4(a)-4(c) show the configuration of the iron core 13 and FIG. 5 shows the configuration of one of the laminated iron plates 14. In FIG. 4(b), a straight line 16 shows the direction in which the iron plates are laminated. Wedge-shaped stuffings 15 are employed to form the fan-shaped iron core 13. As shown in FIG. 6, the wedge-shaped stuffing 15 is formed in such a manner that shifted iron plates are laminated, and offers strength slightly lower than what is provided by an ordinary laminate. The laminated iron plates 14 are laminated between the wedge-shaped stuffings 15. The wedge-shaped stuffings 15 are disposed at equal intervals within the iron core 13 and form the fan-shaped laminated iron core. Each of the both ends of the iron core shown in FIG. 4(b) corresponds to a part of the radius of the arc of the fan-shaped core.
In the conventional synchrotrons as described above, more than six bipolar electromagnets are used, which makes synchrotrons large in size and expensive. It is necessary to decrease the number of bipolar electromagnets to make the apparatus compact. However, the problem may arise that the charged particles are forced to collide with the wall of the vacuum chamber and are lost, because the deflection angle of each bipolar electromagnet must be enlarged so that the focusing action to the charged particles in the horizontal direction increases.
An other problem is that, since the kicker 9 and perturbator 5 are arranged on the same linear portion, a connection means such as a flange should be installed therebetween provided each of them is contained in a different vacuum chamber, and the prolonged linear portion makes it difficult to reduce the size of the apparatus.